Coreopsis, like this Sunfire variety, is a good perennial choice for planting in early fall. (Photo by Allen Owings)

Homestead Purple is the top-performing perennial verbena in LSU AgCenter evaluations. (Photo by Allen Owings)

News Release Distributed 09/05/14

By Allen Owings
LSU AgCenter horticulturist

HAMMOND, La. – Perennials are plants that live for three or more years and often require two or more years from seed to flower. Gardeners are showing renewed interest in non-woody, herbaceous perennials because they often need less maintenance, less water and fewer pesticides than annual bedding plants.

Perennials are easily used as ground covers, mixed with annuals, grown in containers and used as accents or specimen plants. Many perennials are short-season bloomers and are best mixed with others that bloom at different times as part of an overall design.

If you want to plant perennials, consider the site before selecting your plants. Although many perennials, such as ferns, tolerate heavy shade, most perennials require abundant sunshine. Air circulation is important, too, for avoiding diseases; stagnant, warm, humid air creates ideal conditions for diseases. Perennial plants also require properly prepared soil, and a few have specific drainage and fertility requirements.

Though most perennials may take a couple of years from seed to flower, many are as easily started as annuals. The quickest way to have blooming plants, however, is by vegetative propagation, such as by dividing old plants or rooting stem cuttings.

Plants produced vegetatively, rather than by seeds, have all of the traits of the original plant. Propagation by division may seem difficult at first, but most gardeners find that dividing crowns and roots and separating bulbs take little experience and can be mastered quickly. Try dividing monkey grass for experience, then move on to daylilies, and before long you’ll have the hang of it.

Perennials with shallow roots are easily pulled apart by hand. Long, fibrous roots can be pulled apart with a hand fork. Thickly intertwined roots may need more forceful separation or cutting with digging forks. Once they’re divided, replant only those segments with strong roots and at least a few intact leaves or crowns.

In general, it is best to divide perennials during their dormant or "off" season; divide spring-bloomers in fall and fall-bloomers in spring. Some perennials may need dividing every three or four years or else they will slowly crowd themselves into clumps of nonflowering leaves and roots.

Many perennial plants may be propagated from stem cuttings, which do not disturb the plants’ roots. Wait to take stem cuttings during spring or early summer, choosing stems that are mature and firm but not yet hardened and woody. Cut off 4- to 6-inch segments, using a sharp knife or shears, and pinch off the succulent tip and any flower buds to force the cuttings to concentrate their energy on producing roots. Remove the lower leaves that will be below the surface of the rooting medium, but leave a few leaves to provide a source of energy for root initiation and growth.

You may not think about planting perennials this time of the year, but the success of fall through late winter planting is good.

Good choices for herbaceous perennials for Louisiana include lantana, perennial verbena, butterfly bush, Mexican heather, coneflower, rudbeckia, perennial salvia, iris, daylilies, Shasta daisy, coreopsis and many more. Be sure to select perennial flowers appropriate for your particular site and growing conditions. Consult the AgCenter website and select varieties that have been proven superior in AgCenter trials.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren